This invention relates generally to centrifugal compressors and, more particularly, to a method of precompressing the absorptive material in a silencer device to be located in the discharge pipe of a centrifugal compressor.
Centrifugal compressors, of the type which are used for large air conditioning systems, have a number of included 1 components which create sound and vibration that radiates from the compressor and attached components including the motor, gearing, condenser and evaporator shells and the discharge line. In addition to design considerations that tend to minimize these sounds, it is common practice to reduce the sounds by way of external, surface-applied, lagging materials or the addition of internal discharge line silencers (i.e., an acoustically absorptive material such as fiberglass, mineral fiber, or Dacron) which are placed in the discharge line of the compressor. Such an absorptive material is inherently exposed to the flow of compressed fluid through the compressor and, if not protected, tends to be eroded. For example, fiberglass absorbing material that is commonly used is generally quite brittle, and does not hold up well to the movement that it normally encounters in compressor operation unless it is properly preloaded in compression.
One means of protecting the fiberglass absorbing material from erosion is the use of a protective material on either side thereof to stabilize the absorptive material against movement. For example, a perforated metal may be sandwiched on either side of the fiberglass material for that purpose, and screens and fiberglass cloth structures may also be added. However, it has been found that fiberglass cloth also tends to break down, with its particles then entering the system in an undesirable manner. Further, as the erosion of the fiberglass cloth proceeds, it will eventually allow the movement of compressed fluid through the holes of the perforated material to act directly on the enclosed absorptive material and cause it to erode as well. This problem of erosion is further complicated by the requirement that the material for both the absorptive elements and the protective elements be compatible with the refrigerant and lubricant in which they are necessarily immersed.
The usual approach for installing a silencer device in the discharge pipe of a compressor is by rigidly securing the entire assembly to the inner side walls of the discharge pipe by welding or the like. Because of the relatively small size of the discharge pipe and the desirability for placement of the silencer in axial location within the pipe, the accessibility is severely limited to thereby complicate the process. Further, when welding is performed in close proximity to the absorptive material within the silencer device, as is usually required, the absorptive material may be damaged by the resulting heat.
Rather than installing the silencer device directly into the discharge pipe, another approach is to remove a portion thereof and install a complete replacement section comprising a pipe-like structure with the silencer device installed therein. Such a unit has customarily been attached by way of mating flanges. Such an approach is therefore relatively expensive, involving both extensive expenditures of time and material.
In order to obtain the desired performance characteristics in a silencer device, it has often been found necessary to provide a relatively thick absorptive pad in the discharge line. So as to not unduly restrict the flow that would otherwise occur from such a thick pad and its protective elements, a bulbous structure is often provided around the silencer device to thereby reduce the pressure drop thereacross. This, of course, adds substantial expense to the system.
One of the known approaches for eliminating erosion is to preload the absorptive material so that it is less susceptible to movement or vibration when exposed to the flow and pressure conditions encountered in normal compressor operation. This preloading of the material may be accomplished by compressing it in the framework of the silencer structure. This has been accomplished, for example, by installing the fiberglass material into the framework and then, after compressing the framework appropriately, permanently maintaining this compressed position by the use of welding, fasteners, or the like. This process can be time consuming and expensive and can easily result in variable degrees of compression in the absorptive material. Further, it makes it difficult, if not impossible, to replace the fiberglass elements without discarding and replacing the entire silencer framework.
It is therefore an object of the present invention to provide an improved centrifugal compressor silencer apparatus and method of installation.
Another object of the present invention is the provision in a centrifugal compressor silencer for reducing erosion of the absorptive element.
Yet another object of the present invention is the provision in a discharge line silencer of a centrifugal compressor for protecting the absorptive material from erosion.
Another object of the present invention is an improved method of preloading the absorptive material in a centrifugal compressor silencer device.
Yet another object of the present invention is an provision in a centrifugal compressor silencer for a simple method of preloading the absorptive material in a practical and economical manner.
Still another object of the present invention is the provision in a centrifugal compressor silencer for preloading the absorptive material in a uniform manner which allows easy replacement of the absorptive material and reuse of the frame structure therefor.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.